Multi-stage liquid extraction process



United States Patent 3,250,700 MULTI-STAGE LIQUID EXTRACTION PROCESS Reagan E. McChristy, Palos Verdes Estates, Calif, and Carl W. Streed, Mantua Township, Gloucester County, N.J., assignors to Socony Mobil Oil Company, Inc., a corporation of New York No Drawing. Filed May 18, 1962, Ser. No. 195,947 7 Claims. (Cl. 208-320) The present invention relates to a novel process for of saturated hydrocarbons to the extract phase while obtaining a rafiinate phase of relatively low aromatic content. Still more particularly, the present invention relates to such a solvent extraction process for efiective removal, from non-lubricating mineral oil compositions such as kerosene stocks that have been subjected to naphthene dehydrogeneration, of the aromatic hydrocarbons present in such naphthene dehydrogenated kerosense whereby to produce in high yields from such naphthene dehydrogenated materials a highly paratfinic fraction useful as an exceptionally high quality fuel for operation of jet engines.

It is well known to those skilled in the art that liquid sulfur dioxide is a selective solvent for aromatic and unsatur ated hydrocarbons in mixture with saturated hydrocarbons and various methods have been proposed and utilized to eifect extraction of aromatic and unsaturated hydrocarbons from such mixtures with such a selective solvent. Thus, for example, conventional processes have involved the use of a liquid phase process wherein liquid sulfur dioxide is countercurrently contacted with the mineral oil fraction containing aromatic and/or unsaturated hydrocarbons and, more specifically, by feeding liquid sulfur dioxide into the top and the feed stock into the bottom of a suitable tower whereby countercurrent contact is effected to produce a r'afiinate phase discharged from the top of the tower and an extract from the bottom. The raflinate phase, rich in saturated hydrocarbons with some discaolved S0 is then normally treated for removal of S0 which is their recompressed and recycled to the tower; and the extract, rich in aromatics and/or unsaturated hydrocarbons and S0 is also treated for recovery of S0 which is also used for recycle to the tower.

Typical of such conventional operations is the use of pressure suificient to maintain the S0 in liquid phase, temperatures on the order of from about 0 to about +15 F. and use of liquid S0 in from about 50 to about 250, and most usually to 150 vol. percent based on the volume of mineral oil fraction to be solvent extracted. Furthermore, in the use of a plural stage process, wherein the rafi'inate from the first stage from S0 extraction is subjected to a second stage extraction with such a solvent, the same or similar conditions of operation are generally used, and mainly with respect to temperatures. In general, such processes are carried out to produce a raffinate of substantially reduced aromatic and/or unsaturated hydrocabon concentration, base on the feed stock, without regard to the yield of the saturated hydrocarbons and this is particularly so when it is desired to provide a rafiinate substantially devoid of or containing not more than about 10% of aromatic hydrocarbons. As is apparent from the description of this invention as is set forth hereinafter, a novel process has 3,250,733 Patented May 10, I966 been provided whereby in simplified manner a mineral oil fraction containing saturated hydrocarbons in mixture with aromatic and/or unsaturated hydrocarbons can be solvent extracted with liquid S0 to provide a raffinate phase, substantially devoid of or containing not more than about 3 volume percent of aromatic hydrocarbons, in a substantially high yield based on the content of saturated hydrocarbons of the feed stock to the process.

In accordance with this invention, a mineral oil fraction containing saturated hydrocarbons and aromatic and/ or other unsaturated hydrocarbons is subjected to a first stage extraction with liquid S0 and the rafiinate from the first stage extraction is subjected to a similar extraction with liquid S0 but at a substantially higher temperature than the first stage. As to the first stage, the temperature that is employed is restricted to that above the pour or freeze point of the charge stock to be solvent extracted and, in particular preferred embodiments, the present invention is practiced with charge stocks that have a pour point below 'l0 F. whereby the first stage is carried out at a temperature above the pour point of the charge stock but not in excess of about +10 F. Where appropriate, the first stage is carried out at as low a temperature as is practical commensurate with the pour point of the charge stock. As to the proportional amount of liquid S0 to the charge for the first stage operation, a large amount (volume percent) of liquid S0 is used, based on the volume of the feed stock, and in general, from about 150 to about 300 volume percent of liquid S0 based on the volume of the feed stock. The rafiinate from the first stage is then subjected to a similar extraction step with respect to proportional amount of liquid S0 to raffinate but at a substantially higher temperature than the first stage and, in general, a temperature of at least 15 F., and preferably at least 20". F., higher than used for the first stage. Normally, the S0 present in the railinate from the first stage is removed prior to the second stage extraction but such removal of S0 is not essential. By use of such a plural stage process at such a temperature differential between the two stages, it has been found that the selectivity of the extraction by liquid S0 is markedly increased whereby highly effective extraction of aromatics and/or other unsaturated hydrocarbons is provided with retention to an unexpected extent of the desired saturated components, i.e., the loss of the desired saturated hydrocarbons to the extract phase is minimized in the two step process.

For the process embodied herein to provide a combination ofhigh rafiinate yields with low aromatic con-- tent, there may be used any of many mineral oil feed stocks containing saturated hydrocarbons and aromatic and/or other unsaturated hydrocarbons and from which it is desired to extract the aromatic and/or the other unsaturated hydrocarbons with the saturated hydrocarbons being the more valuable product, or vice versa. Thus, the process may be used for mineral oil fractions such as appropriate mineral oil distillates to produce high cetane number diesel fuels, highly .aromatic specialty solvents, highly parafiinic specialty solvents, or any hydrocarbon material wherein a high concentration of either aromatic and/or unsaturates or saturates is desired. In particular, the process embodied herein is particularly adapted to treatment of appropriate mineral oil distillates for preparation of fuels for jet engines and, more particularly, to fractions in the boiling range of kerosenes to remove aromatics and/or other unsaturated hydrocarbons therefrom to produce exceptionally high quality jet fuels in unexpectedly high yields from an S0 3 fractions boiling in the range of from about 350 to about 550 F. and containing the following hydrocarbons: parafiins, naphthenes and aromatic hydrocarbons; narrow kerosene cuts boiling in the range of from about 375 to about 525 F. and containing a mixture of such hydrocarbons; and for preparation of jet fuels of exceptionally high quality, kerosene fractions boiling in the aforesaid ranges that have been subjected to naphthene dehydrogenation to convert all or a substantial amount of the naphthenes to aromatics whereby to produce, as the feed stock for the process embodied here'm, a dehydrogenated kerosene fraction composed substantially of paraffins and aromatics and, depending on the extent to which the naphthene dehydrogenation was efiected, a minor amount of naphthenes. Generally, such dehydrogenated kerosenes' contain a small amount of olefinic hydrocarbons but, when present, in amounts that normally do not exceed about 3.0%.

In further reference to virgin kerosenes useful as feed stocks for'the process embodied herein, such kerosenes can be derived from a variety of crude sources including Mid-Continent, Barco, West Texas, and Middle East (Kuwait) and which kerosenes may contain parafiins, naphthenes and aromatics in the following amounts, in weight percent; from about 30 to about 70 paraffins, from about 20 to about 50 naphthenes, and from about 5 to about 30 aromatics. Specific embodiments include straight run kerosene fractions of the following composition:

ASTM boiling range (375500 F.) Mid-Continent Barco W. Texas Wt. Vol. Wt. Vol. Wt. Vol.

Parafiins 39. 9 42. 7 42. 4 45. 1 58. 6 61. 1 Naphthene 43. 1 42. 1 43. 3 42. 0 33. 2 31. 8 Aromatics. 17. 0 15. 2 l4. 3 12. 9 8. 2 7. 1

In reference to use, for the feed stocks to the process embodied herein, of such kerosenes that have been subjected to naphthene dehydrogenation 'to convert a substantial amount of the naphthenes to aromatics, the following are compositions of such naphthene dehydrogenated kerosenes (375515 F. fractions) derived from the aforesaid specifically defined virgin kerosenes:

In general, however, and with respect to naphthene dehydrogenated kerosenes, the process embodied herein is carried out with such kerosenes boiling in the range of from about 350 to about 570 F., of the following composition:

Vol. percent Parafiins From about 35 to about 70. Naphthenes From about 1 to about 2-0. Aromatics From about 25 to about 60.

In order to further describe the invention, the following' embodiments are set forth for purposes of illustration and not limitation. For the embodiments set forth, including for purposes of comparison the results obtained from an S0 extraction carried out in conventional manner, the process was carried out in liquid phase in a contacting tower of conventional design in which the liquid S0 was fed to the top portion of the tower and the mineral oil fraction to the bottom portion of the tower with obtainment of a raffinate withdrawn from the top of the tower and an extract phase from the bottom.

Example 1 Charge to extraction: Dehydrogenated West Texas kerosene of the following composition boiling in the range of 407 to 538 F.

' Vol. percent Parafiins 62.2 Naphthenes 5.1 Olefins 2.8 Aromatics 29 9 Two pass operation Convenof present invention SO 'unit operating conditions tional one pass operation First Second Pass Pass Charge rate (barrel/day of dehydrogenated kerosene) 3, 000 3, 3, 500 Vol. percent of S0 feed- 240 250 200 Temperature, F +44 0 +42 Yields, per pass:

Raflinate, vol. percent. 51 6o 94 Extract, vol. percent 4.9 35 6 Yields, overall:

Raffinate, vol. percent 1 51 2 61 Extract, vol. percent 1 49 2 39 Two Pass Operation of Present Invention First Pass Second Pass Feed Rafii- Extract Feed Rafii- Extract 2 nate hate 2 Gravity, API 42. 7 52. 1 27.6 52. 1 52. 5 46. 3 Aniline pt., 9 11.-.- 135. 3 181. 0 10. t 181. 0 184. 7 135. 5 Aromatics content,

percent vol 31. 2 2. 7 84. 0 2. 7 1. 2 26. 2

Properties of feed, ratlinate and extract from the conventional one stage operation: 7

Material Feed Raflinate Extract Gravity, API 43. 1 52. 9 32. 6 Aniline pt-., F 134. 4 184. 1 58. 5 Aromatic content, vol.

percent 1. 29. 9 1. 7

2 Loss of raflinate to extract in two pass operation:

Bls./l,000 bls. of feed 86 Percent of total potential 172. 3

Process efficiency, vol. percent of total potential ra-flinate that was actually recovered f 7. 7

Norn.Loss of desired raflinate components to extract: 189 barrels per 1000 barrels of feed, or 27.0 percent of the total potentially available rafiinate components, i.e., the process efficiency in terms of the total desired raffinate components present in the original dehydrogenated kerosene that was actually recovered as final product was 73.0 percent.

were lost to the extract in the process of this invention. v

As is further apparent from the data in Example 1, the raifinate obtained in the markedly higher yield from the two pass operation was of exceptionally high quality in that the aromatic content was 1.2% (vol) thereby providing in such high yield a highly paraffinic fraction useful as an exceptionally high quality jet fuel.

Example 2 The following data illustrates the marked improve ment obtained by practice of the two stage process, embodied herein utilizing a relatively lower temperature 7 for the first stage than the second stage as compared to 5 results typical of those obtained from a conventional operation using two stages but at the same temperature.

Feed stock: Dehydrogenated Gach Saran kerosene of the following composition boiling in the range of 400 to Dehydrogen- Dehydrogenated West ated Gach Texas kerosene Saran kerosene Aromatic content 29. 9 38. 9

Yield increases, present process over conventional process, percent- 19 47 534 F. Although the present invention has been described with Gravity, API 39.4 preferred embodiments, it is to be understood that modi- Aniline pt., F. 130 fications and variations may be resorted to, without de- Aromatics content, vol. percent 38.9 parting from the spirit and scope of this invention, as

Process of the present invention Conventional operation First pass Second pass First pass Second pass SO -Unit operating conditions:

Charge rate, bls./day of kerosene 3, 500 3, 500 3, 500 3, 500 80;, percent vol. of hydrocarbon feed to extion unit." 200 200 240 240 Temp, F 4 +44 +44 +44 Yields per pass:

Rafiinate, vol. percent. 57 94 35. 9 89. 7 Extract, vol. percent 43 6 64.1 10.3 Yields, overall:

Ratfinate, vol. percent 53. 5 32. 2 Extract, vol. percent; 46. 5 67. 2

Feed Rafiinate Extract Feed Rafiinate Extract Feed Raffinate Extract Feed Rafiinate Extract Properties:

Gravity, API 39. 4 51. 0 26. 2 51. 9 51. 5 45. 0 39. 4 50. 9 33.4 50. 9 51.7 45. 1 Aniline pt.,f F 130.0 176. 4 8. 4 176. 4 180. 7 135. 0 130. 0 175. 4 56. 0 175. 4 180. 9 134. 8 Aromatic content, vol.

percent 88. 9 3. 5 85. 9 3. 5 1. 1 29 38. 9 4. 0 60 4. 0 1. 0 30 Loss of desired raflinate components to extract:

Bls./1000 bls. of feed 84.8 289 Percent of total potential" 13. 9 47. 4 Process elficiency, vol. percent of total potential recovered (desired raflinate compo nents) 86. 1 52. 6

In practice of this invention, it should be apparent to those skilled in the art that the process embodied herein can be carried out with use of more than two stages for extraction with S0 as long as there is employed two stages of extraction using successively a relatively low and a relatively higher extraction temperature. However, for'most purposes, and as is evidenced by the foregoing description of the invention, a two stage extraction is satisfactory.

Moreover, in practice of this invention, it may be desirable for certain applications to carry out the process embodied herein by subjecting an appropriate feed stock to a first stage extraction with liquid S0 at a relatively low temperature to provide a first raflinate and an extract and charging only a portion of the first raflinate to a second stage extraction at a higher temperature than the 0 first stage. For such a process, and for example, the operating conditions for the second extraction may be correlated to produce a raflinate of exceptionally low aromatic content (e.g., not more than about 1 to, 2% vol.) and which raffinate can be blended with the remaining portion of the raffinate from the first extraction to produce a blended raffinate product to meet the aromatic content depending on specifications for particular jet fuels.

An important aspect of the discovery on which the present invention is based is that, generally speaking, the advantage in yield of desired rafiinate components increases as the aromatic content of the charge stock to the process is increased. In illustration, the following is typical of the increase in yield that .is obtained by practice of this invention, as compared to results from a conventhose skilled in the art will readily understand. Such variations and modifications are considered to be within the purview and scope of the appended claims.

What is claimed is:

1. A two stage liquid phase selective solvent extraction process for separating liquid hydrocarbon mixtures of saturated hydrocarbons and unsaturated hydrocarbons into a raffinate phase rich in saturated hydrocarbons and an extract phase rich in unsaturated hydrocarbons with minimized loss of saturated hydrocarbons to the extract phase which comprises subjecting a liquid hydrocarbon mixture, having a pour point below -l0 F. and boiling in the range of from about 350 to about 570 F., of saturated hydrocarbons and unsaturated hydrocarbons to a first contact with liquid sulfur dioxide at a temperature above the pour point of said mixture but not in excess of about 10 F. to produce a first raffinate rich in saturated hydrocarbons and a first extract rich in unsaturated hydrocarbons, and subjecting said first ralfinate ,to a second contact with liquid sulfur dioxide at a temperature of at least about 15 F. higher than the temperature of said first contact to produce a second rafiinate substantially richer in saturated hydrocarbons than said first rafiinate.

2. A process, as defined in claim 1, wherein the liquid hydrocarbon mixture is a non-lubricating mineral oil fraction.

3. A process, as defined in claim 1, wherein the liquid hydrocarbon mixture is a kerosene fraction.

4. A process, as defined in claim 1, wherein the liquid hydrocarbon mixture is a naphthene dehydrogenated kerosene fraction containing, in volume percent, from about 35 to about 70 parafiins, from about one to about naphthenes, and from about to about aromatics.

5. A process, as defined in claim 1, wherein said contacts with the liquid sulfur dioxide are carried out with an amount of from about 150 to about 300 volume percent of sulfur dioxide based on the volume of the liquid hydrocarbon subjected to contact with the sulfur dioxide.

6. A two stage liquid phase extraction process for separating liquid hydrocarbon mineral oil mixtures boiling in the range of from about 350 to about 570 F, having a pour point below 10 F., and containing, in volume percent, from about 35 to about paraflins, from about 1 to about 20 naphthenes and from about 25 to about 60 aromatics into a (1) rafiinate phase rich in saturated hydrocarbons and containing not more than about 3 volume percent aromatics and (2) an extract phase rich in unsaturated hydrocarbons with minimized loss of saturated hydrocarbon components of said liquid mixture to said exthe first rafiinate to a second contact with liquid S0 at a temperature of at least about 15 F. higher than the temperature of said first contact to produce a second raffinate rich in saturated hydrocarbons and containing not more than about 3 volume percent unsaturated hydrocarbons.

7. A process, as defined in claim 6, wherein the said contacts with the liquid S0 are carried out with an amount of liquid S0 of from about to about 300 volume percent based on the volume of liquid hydrocarbons subjected to contact with the liquid S0 References Cited by the Examiner UNITED STATES PATENTS 2,116,540 5/1938 Roberts 20s 320 2,671,046. 3/1954 .Arnold et al. 208-317 OTHER REFERENCES Moore et al.: Met. and Chem. Eng, vol. 18, No. 8, pp. 396-402 (April 15, 1918).

DELBERT E. GANTZ, Primary Examiner. ALPHONSO D. SULLIVAN, Examiner. P. P. GARVIN, H. LEVINE, Assistant Examiners. 

1. A TWO STAGE LIQUID PHASE SELECTIVE SOLVENT EXTRACTION PROCESS FOR SEPARATING LIQUID HYDROCARBON MIXTURES OF SATURATED HYDROCARBONS AND UNSATURATED HYDROCARBONS INTO A RAFFINATE PHASE RICH IN SATURATED HYDROCARBONS AND AN EXTRACT PHASE RICH IN UNSATURATED HYDROCARBONS WITH MINIMIZED LOSS OF SATURATED HYDROCARBONS TO THE EXTRACT PHASE WHICH COMPRISES SUBJECTING A LIQUID HYDROCARBON MIXTURE, HAVING A POUR POINT BELOW -10*F. AND BOILING IN THE RANGE OF FROM ABOUT 350 TO 570*F., OF SATURATED HYDROCARBONS AND UNSATURATED HYDROCARBONS TO A FIRST CONTACT WITH LIQUID SULFUR DIOXIDE AT A TEMPERATURE ABOVE THE POUR POINT OF SAID MIXTURE BUT NOT IN EXCESS OF ABOUT 10*F. TO PRODUCE A FIRST RAFFINATE RICH IN SATURATED HYDROCARBONS AND A FIRST EXTRACT RICH IN UNSATURATED HYDROCARBONS, AND SUBJECTING SAID FIRST RAFFINATE TO A SECOND CONTACT WITH LIQUID SULFUR DIOXIDE AT A TEMPERATURE OF AT LEAST ABOUT 15*F. HIGHER THAN THE TEMPERATURE OF SAID FIRST CONTACT TO PRODUCE A SECOND RAFFINATE SUBSTANTIALLY RICHER IN SATURATED HYDROCARBONS THAN SAID FIRST RAFFINATE. 